Electron multiplier

ABSTRACT

954,247. Electron multipliers; electrode materials. BENDIX CORPORATION. Nov. 10, 1961 [Nov. 15, 1960], No. 40373/61. Heading H1D. An electron multiplier comprises at least one magnetic member 20 having a surface 24 with north and south poles along opposite longitudinal sides of it, means for establishing a continuous voltage drop along said surface, another member 22 with a surface 26 facing said first surface, means for establishing another continuous voltage drop along said second surface such that opposite points of both surfaces are at unequal electric potentials to create an electric field whose equipotential lines are oblique to said surfaces, at least one of said surfaces 26 further being secondarily emissive, so that under the joint action of said electric and magnetic fields secondary electrons are accelerated along said secondarily emissive surface. Preferably both members 20, 22 are magnetic with like poles facing each other, composed of rectangular plates of ferrite, and polepieces 34, 36, Fig. 3, may be provided to reduce the reluctance of the magnetic circuit, being separated from the magnets by strips 30, 32 of trifluorochloroethylene. Positive ions or ultra violet radiation incident through a window 40 strike the cathode 28, releasing secondary electrons which follow a cycloidal path 57, increasing in number with each impact with the surface 26, and are finally collected on the anode 42. The secondary emissive material is preferably antimony tin as described in Specification 954,246 and when used to detect ultra violet radiation the cathode 28 is preferably of tungsten, nickel or platinum.

Dec. 21, 1965 R. THOMPSON 3,225,239

ELECTRON MULTIPLIER Filed Nov. 15, 1960 42 57 2O 24 56 28 -l7OO V VOLTAGE SOURCE 28 22 so f 3 FIG.4

INVENTOR. ROBERT R. THOMPSON ATTORN Y United States Patent 3,225,239 ELECTRON MULTIPLIER Robert R. Thompson, Livonia, Mich., assignor to The Bendix Corporation, Southfield, Mich., a corporation of Delaware Filed Nov. 15, 1960, Ser. No. 69,455 8 Claims. (Cl. 313-103) This invention pertains to an electron multiplier of the kind where electrons are' caused to cycloid by magnetic and electric fields against a secondary emissive surface, wherein the means for establishing the magnetic field are used to establish the electric field, making unnecessary separate electric field strips and dynode strips.

It is an object of this invention to provide such an electron multiplier having a pair of closely spaced permanent magnets having their north poles aligned and their south poles aligned to provide magnetic lines of force between the plates and between the north and south poles. The magnets may be coated with a resistive material and a voltage source may be connected to the coatings to establish electric currents in the coatings transverse to the magnetic lines of force. Charged particles, then may be introduced between the magnetic plates and caused to cycloid against one of the resistive surfaces, resulting in a multiplying action.

This and other objects will become more apparent when preferred embodiments are considered in connection with the drawings wherein:

FIGURE 1 is a plan view of a preferred embodiment of this invention;

FIGURE 2 is a section taken at 2-2 of FIGURE 1;

FIGURE 3 is an end view of FIGURE 2; and

FIGURE 4 is an end View of an embodiment wherein the magnetic plates are separated by spaced posts instead of a continuous strip of insulation.

Looking at the drawings, and especially'FIGURES 1, 2 and 3, is seen a pair of magnets 20, 22, which may be of a ferrite material such as BaO-6Fe O each of which has a coating 24, 26 of antimony tin on their inner sides. A further coating is formed on the lower magnet 22 and provides a cathode 28. This coating may also be antimony tin but for ultra violet photon detection, for which this embodiment is particularly adapted to, tungsten, nickel, or platinum is preferable.

Permanent magnets 20, 22 have their north and south poles aligned as indicated in FIGURE 3, with the two north poles at the left side of the magnets and the two south poles at the right side of the magnets, so that a magnetic field is created between the magnets from the north pole side to the south pole side.

Separating the magnets 20, 22 a distance of .2" are longitudinal strips 30, 32 made of a polymer of trifiuorochloroethylene, each having a pair of longitudinal grooves formed therein to receive the north and south pole sides of magnets 20, 22. Bolted or otherwise connected to each strip 30, 32 is a polepiece 34, 36, of soft iron or other magnetic material. The polepieces 34, 36 form part of the magnetic circuit and reduce the reluctance of the path of magnetic lines of force. Bolted to insulation strips 30 and 32 on the upper surface of the multiplier and approximately horizontally aligned with upper magnet 20, is a grid frame 38 which contains at the center part thereof a nickel mesh 40 which is substantially above and vertically in line with cathode 28. Located at the opposite end of the multiplier is an anode 42 which is bolted or otherwise fixed to an end section 44 of insulative material. Also, there is an end section 46 of insulative material between the right ends of the multiplier. Connected through insulation 44 to anode 42 is a micro ammeter 50.

3,225,239 Patented Dec. 21 1965 A voltage source 48 supplies a large negative voltage, such as a --2000 volts, to one end of coating 26, cathode 28, and potentiometer 52. The other end of potentiometer 52 is connected to grid 40 and the potentiometer is set so that the potential applied at grid 40 is a 1700 volts. Grid 40 is in electrical connection with resistive coating 24 and, hence, a potential of approximately 1700 volts exists at the right end of coating 24 and the other end of coating 24 may be grounded so that its potential is zero. The coating 26 on the lower magnet 22 is connected at one end to the -2000 volt potential source 48 and at the other end to a potentiometer 54 which is set so that the voltage at the other end is approximately a 300 volts. This provides an electric field having equipotential lines which are slanted from top to bottom as shown by lines 56 and which combine with the transverse magnetic field to cause electrons to travel in a cycloidal path 57 against coating 26. Each cycloid results in secondary emission, or freeing of electrons from the surface of coating 26, thereby multiplying the number of electrons according to the characteristics of the cycloid and the coating 26. The above voltage valu are, of course,only representative.

Operation In the operation of this embodiment charged particles such as positive ions or ultra violet photons are introduced to grid 40 and are accelerated to cathode 28 since it is at a lower potential. This causes secondary emission from cathode 28 of electrons which are attracted between the magnets 20 and 22, and due to the electric and magnetic fields existing between the plates, are caused to cycloid along the lower surface coating 26. Each cycloid causes a multiplication of electrons. The electrons impinge upon anode 42 where the current may be read by ammeter 50 or used in another manner.

If desired, the magnets 20 and 22 could be used without any resistive coating, utilizing the current carrying and secondary emissive properties of the magnet material itself.

An end view of a second embodiment is shown in FIG- URE 4 wherein spaced insulative posts 60 are used to separate magnets 20 and 22 on each side. Posts 60 replace the continuous insulative strips 30 and 32 and pole piec s 34, 36 but otherwise the multiplier shown in FIG- URE 4 is the same as that shown in FIGURE 3. This provides a magnetic field which may be desired for cer tain applications.

Although this invention has been disclosed and illustrated with reference to particular applications, the principles involved are susceptible of numerous other applications which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

Having thus described my invention, I claim:

1. A multiplier apparatus for receiving and multiply ing charged particles comprising at least one magnet means having a north pole and a south pole with lines of magnetic force extending between said poles,

a secondary emissive resistive coating being on a surface of said one magnet means,

the material of said one magnet means on which said secondary emissive resistive coating is formed having a resistance greater than said resistive coating,

a voltage source connected across said secondary resistive surface in a direction substantially perpendicular to a line between said north pole and said south pole,

said voltage source causing current to flow through said resistive secondary emissive coating,

said voltage source supplying an electric field having a component perpendicular to the surface of said one magnet means to cause charged particles including electrons to cycloid into the surface of said magnet means,

and means for collecting the charged particles.

2. The apparatus of claim 1 with a second magnet means having a north and south pole aligned, respectively, with the north and south pole of said one magnet means and being closely spaced to the secondary emissive resistive surface of said one magnet means,

the north pole of said second magnet means being adjacent the north pole of said one magnet means and the south pole of said second magnet means being adjacent the south pole of said one magnet means with the magnetic lines of force being between and substantially parallel to said one and said second magnet means,

a secondary emissive resistive coating being on the sur* face of said second magnet means which is facing the secondary resistive surface of said one magnet means,

said voltage source being connected across said secondary emissive resistive surface of said second magnet means in a direction substantially perpendicular to a line between said north pole and said south pole.

3. The apparatus of claim 2 with the potentials applied by said voltage source to said secondary emissive resistive surfaces establishing an electric field which is inclined to the surface of said one magnet means,

the planes formed by said lines of force of said electric field and the projections of said lines on said one magnet means surface being substantially perpendicular to the magnetic lines of force.

4. The apparatus of claim 2 with grid means being coplanar with said second magnet means,

means for placing said grid at a potential relative to said one magnet means to accelerate said charged particles towards said one magnet means.

5. The apparatus of claim 4 with cathode means being placed adjacent said one magnet means and opposite said grid means so that it is in the path of said charged particles,

said cathode means emitting electrons when struck by said charged particles.

6. The apparatus of claim 2 with a magnetic pole piece being adjacent and between the north poles of each of said magnet means and a magnetic pole piece being adjacent and between the south poles of each of said magnet means,

insulation being between each of said magnet means and said pole pieces.

7. A multiplier apparatus for receiving and multiplying charged particles comprising at least one magnet means having a north and south pole with lines of magnetic forces extending between said poles,

a voltage source connected across said magnet means in a direction having a substantial perpendicular component to a line between said north pole and said south pole,

said magnet means having a secondary emissive resistive surface,

said voltage source causing current to flow through said secondary emissive resistive surface,

said voltage source supplying an electric field having a component perpendicular to the secondary emissive surface of said magnet means to cause charged particles including electrons to strike the secondary emissive surface of said magnet means in a plurality of successive multiplication stages,

and means for collecting the charged particles.

8. The multiplier of claim 7 with a second magnet means having a secondary emissive resistive surface and a north and south pole being aligned, respectively with the north and south poles of said first magnet means,

said voltage source connected across said second magnet means in a direction having a substantial component to a line between said north and south pole of said second magnet means,

said voltage source causing an electric field to be formed between said magnet means.

References Cited by the Examiner UNITED STATES PATENTS 2,983,845 5/1961 Damoth et al. 313-103 X JOHN W. HUCKERT, Primary Examiner.

RALPH G, NILSON, ARTHUR GAUSS, Examiners. 

1. A MULTIPLIER APPARATUS FOR RECEIVING AND MULTIPLYING CHARGED PARTICLES COMPRISING AT LEAST ONE MAGNET MEANS HAVING A NORTH POLE AND A SOUTH POLE WITH LINES OF MAGNETIC FORCE EXTENDING BETWEEN SAID POLES, A SECONDARY EMISSIVE RESISTIVE COATING BEING ON A SURFACE OF SAID ONE MAGNET MEANS, THE MATERIAL OF SAID ONE MAGNET MEANS ON WHICH SAID SECONDARY EMISSIVE RESISTIVE COATING IS FORMED HAVING A RESISTANCE GREATER THAN SAID RESISTIVE COATING, A VOLTAGE SOURCE CONNECTED ACROSS SAID SECONDARY RESISTIVE SURFACE IN A DIRECTION SUBSTANTIALLY PERPENDICULAR TO A LINE BETWEEN SAID NORTH POLE AND SAID SOUTH POLE, SAID VOLTAGE SOURCE CAUSING CURRENT TO FLOW THROUGH SAID RESISTIVE SECONDARY EMISSIVE COATING, SAID VOLTAGE SOURCE SUPPLYING AN ELECTRIC FIELD HAVING A COMPONENT PERPENDICULAR TO THE SURFACE OF SAID ONE MAGNET MEANS TO CAUSE CHARGED PARTICLES INCLUDING ELECTRONS TO CYCLOID INTO THE SURFACE OF SAID MAGNET MEANS, AND MEANS FOR COLLECTING THE CHARGED PARTICLES. 